OpAMP - fix identyfing attributes

[Kielek]

From autoinstrumentation implementation, following attributes are considered as identyfiing
public const string AttributeServiceName = "service.name";
public const string AttributeServiceInstanceId = "service.instance.id";
public const string AttributeServiceNamespaceName = "service.namespace.name";

Can we/should we add others?

Originally posted by @Kielek in open-telemetry/opentelemetry-demo#3656 (comment)

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I think that service.namespace.name was wrongly implemented.